The overall objective of this contract is to provide a resource for preclinical in vitro evaluation of new chemical substances against members of the herpesvirus group -- herpes simplex virus type 1 (HSV-1), herpes simplex virus type 2 (HSV-2), cytomegalovirus (CMV), varicella-zoster virus (VZV), and Epstein-Barr virus (EBV). In the initial studies, experimental compounds will be screened using the CPE inhibition assay in HFF cells against standard laboratory-adapted strains (except EBV). Initial cytotoxicity will be assessed in HFF cells by both cell proliferation study and neutral red uptake assay. The initial EBV screen will be to measure the VCA or EA production by the immunofluorescence assay in Daudi or Raji cells superinfected with P3HR-1 EBV. Substances that have a selectivity index of ten or greater will be confirmed using additional assay systems. Antiviral activity (except activity against EBV) will be confirmed by the plaque inhibition assay in HFF cells and in other cells derived from non-human sources. The anti-EBV activity will be confirmed by using the DNA hybridization assay to measure the inhibition of DNA synthesis in P3HR-l cells. This battery of confirmatory tests is designed to select substances that have potential for further evaluation in animal models and clinical trials. Substances that are selected for additional follow-up studies will be evaluated in a number of different systems, including: (1) susceptibility to additional laboratory passaged viral strains and clinical isolates, including drug-resistant mutants; (2) combination chemotherapy with other antiviral agents; (3) mechanism of action studies; and (3) evaluation of toxicity using a bone marrow clonogenic assay.